This invention relates generally to apparatus for measuring the crystallographic orientation (angle of cut) of already manufactured single crystal plates, such as quartz resonator plates, of singly and double rotated cuts. The angles of cut of double rotated plates can be described by the IEEE notation of (YXWl) .phi./.theta.. This notation is explained in "Standards on Piezoelectric Crystals, 1949" , Proc, IRE, Vol. 37, Dec. 1949, pp. 1378-1395, and in IEEE Standard No. 176 incorporated herein by reference. An SC-cut, for example, may be described as (YXWl) 22.43.degree./34.31.degree.. For simplicity, a cut may also be described by stating the two rotation angles only, e.g. .phi.=22.43.degree., .theta.=34.31.degree. describes the same SC-cut. Orientation in the plane of the plate shall be denoted by .psi., which is an angle measured from the X"-axis. Definitions of the various cuts can be found in the references. For purposes of these guidelines, the AT and SC-cuts shall be defined as the .phi.=0.0.degree..+-.0.4.degree. and .phi.=22.0.degree..+-.0.8.degree. cuts respectively on the .phi.&gt;0 branch of the bulk wave zero temperature coefficient locus.
For the case of singly rotated cuts, such as the AT-cut, automated single axis, double crystal X-ray diffractometers are readily available with sufficient accuracy to attain high manufacturing yield. Details of one such system are described in U.S. Pat. No. 4,065,211. However, a practical apparatus to determine the angle of cut of "doubly rotated" cuts, such as the SC-cut, has not been available prior to this invention. Such a device employing a monochromatic X-ray source would require a complex goniometer with at least three axes of rotation.
Double rotated quartz crystal resonators, particularly the SC-cut have been shown to have smaller frequency shifts induced by mechanical stresses in the plane of the resonator than the single rotated AT-cut resonators. These cuts have also been shown to be less sensitive to the thermal stresses produced by sudden temperature changes. Doubly rotated quartz cuts, therefore, have the potential for providing resonators of superior stability with respect to vibration, oven temperature fluctuations, temperature cycling (in ovenless applications), and time. (e.g., long term aging). To produce doubly rotated blanks, two angles must be specified and controlled to a high degree of accuracy during the manufacturing process. Therefore if the superior qualities of the SC-cut are to be realized on a large scale, there need be, as a minimum, crystal plate orientation and measurement apparatus with adequate throughput capability and sufficient accuracy to permit high yield manufacture.